linux-kernel - [PATCH v2 2/3] cpufreq: qcom: fix writes in read-only memory region

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Message-Id: <20221015130424.1923706-2-fabien.parent@linaro.org>
Date:   Sat, 15 Oct 2022 15:04:23 +0200
From:   Fabien Parent <fabien.parent@...aro.org>
To:     ilia.lin@...nel.org, agross@...nel.org, andersson@...nel.org,
        rafael@...nel.org, viresh.kumar@...aro.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-pm@...r.kernel.org, Fabien Parent <fabien.parent@...aro.org>
Subject: [PATCH v2 2/3] cpufreq: qcom: fix writes in read-only memory region

This commit fixes a kernel oops because of a write in some read-only memory:

	[    9.068287] Unable to handle kernel write to read-only memory at virtual address ffff800009240ad8
	..snip..
	[    9.138790] Internal error: Oops: 9600004f [#1] PREEMPT SMP
	..snip..
	[    9.269161] Call trace:
	[    9.276271]  __memcpy+0x5c/0x230
	[    9.278531]  snprintf+0x58/0x80
	[    9.282002]  qcom_cpufreq_msm8939_name_version+0xb4/0x190
	[    9.284869]  qcom_cpufreq_probe+0xc8/0x39c
	..snip..

The following line defines a pointer that point to a char buffer stored
in read-only memory:

	char *pvs_name = "speedXX-pvsXX-vXX";

This pointer is meant to hold a template "speedXX-pvsXX-vXX" where the
XX values get overridden by the qcom_cpufreq_krait_name_version function. Since
the template is actually stored in read-only memory, when the function
executes the following call we get an oops:

	snprintf(*pvs_name, sizeof("speedXX-pvsXX-vXX"), "speed%d-pvs%d-v%d",
		 speed, pvs, pvs_ver);

To fix this issue, we instead store the template name onto the stack by
using the following syntax:

	char pvs_name_buffer[] = "speedXX-pvsXX-vXX";

Because the `pvs_name` needs to be able to be assigned to NULL, the
template buffer is stored in the pvs_name_buffer and not under the
pvs_name variable.

Fixes: a8811ec764f9 ("cpufreq: qcom: Add support for krait based socs")
Signed-off-by: Fabien Parent <fabien.parent@...aro.org>
---

v2:
 * Added missing "Fixes" tag
 * Rebased to not depend on another non-bug fix patch

 drivers/cpufreq/qcom-cpufreq-nvmem.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/qcom-cpufreq-nvmem.c b/drivers/cpufreq/qcom-cpufreq-nvmem.c
index 3bd38acde4b9..82e0339d7722 100644
--- a/drivers/cpufreq/qcom-cpufreq-nvmem.c
+++ b/drivers/cpufreq/qcom-cpufreq-nvmem.c
@@ -265,7 +265,8 @@ static int qcom_cpufreq_probe(struct platform_device *pdev)
 	struct nvmem_cell *speedbin_nvmem;
 	struct device_node *np;
 	struct device *cpu_dev;
-	char *pvs_name = "speedXX-pvsXX-vXX";
+	char pvs_name_buffer[] = "speedXX-pvsXX-vXX";
+	char *pvs_name = pvs_name_buffer;
 	unsigned cpu;
 	const struct of_device_id *match;
 	int ret;
-- 
2.37.2